Conventional automotive braking systems are essentially binary in nature; i.e., the lights are illuminated when the brakes are applied and are not illuminated when the brakes are not applied.
U.S. Patent Publication No. 2010/0085180 describes a brake light system using a potentiometer to sense pedal travel or brake application pressure and to produce a signal illuminating a brake light assembly in a graduated fashion thereby to convey information to a following vehicle driver regarding the driver-initiated braking action of the lead vehicle. This system suffers a number of disadvantages, including variability of actual deceleration display from vehicle to vehicle in the field, and the fact that brake application level, whether represented by pedal displacement or brake line pressure, is not a reliable indicator of actual vehicle deceleration. Greater brake pressure and/or pedal displacement may be needed to produce a given degree or deceleration as the brakes wear or, if fluid is depleted, or as vehicle load increases, or as a consequence of any combination of these factors. Furthermore, the quality of the road surface, tire composition and condition, all affect deceleration and even hard brake application may produce a relatively low deceleration rate on gravel, or wet and/or snow or ice-covered surfaces. If a vehicle is equipped with a regenerative brake energy capture system or a Jake/Exhaust/Retarder system, this may affect the relationship between brake pressure and actual deceleration.